[Az-Geocaching] uploading images

I got my pictures developed at Costco and I got the images on disk option. I am trying to put up some of them on my logs but the keep coming up pixelated, to the point they are un viewable. I tried to upload them directly, but the files are too large. So I reduced the size, but it was unviewable. The next time i tried to reduce the pixel size and the result was the same.
any suggestions, or what am I missing?